1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device. Specifically, the invention relates to a semiconductor device with densely stacked semiconductor chips and a manufacturing method thereof.
2. Description of the Background Art
Most conventional methods of mounting a semiconductor chip(s) have employed die bonding of one semiconductor chip to a single lead frame. Referring to FIG. 36, a semiconductor chip 101 is attached directly onto a die pad 103 integrated with a lead frame by means of adhesive or double-faced tape. A terminal electrode (not shown) of the semiconductor chip and a lead terminal 104 are connected by a wire 105 and they are further encapsulated by an encapsulating resin for the purpose of protection from moisture, impact and the like. Although this type of semiconductor device can be manufactured in a simple manner and its many advantages have been proved, it has a problem of a low ratio of the semiconductor chip relative to a unit volume in which the semiconductor chip is housed.
Accordingly, as shown in FIG. 37, a semiconductor device has been proposed including two stacked semiconductor chips 101a and 101b (Japanese Patent Laying-Open No. 2000-156464). This semiconductor device includes a lower semiconductor chip 101b attached to one frame 104a by adhesive 107 and an upper semiconductor chip 101a attached to the other frame 104b. The semiconductor chips are further bonded to each other by adhesive 107. Respective terminal electrodes (not shown) of the semiconductor chips and lead terminals (not shown) are connected by means of wires (not shown) and encapsulated by an encapsulating resin 106. In plan view, the semiconductor chips of the semiconductor device shown in FIG. 37 mostly overlap one another with a small displacement therebetween. In this way, the semiconductor device shown in FIG. 37 achieves a dramatic densification as compared with the semiconductor device shown in FIG. 36.
Through never-ending progress in downsizing of semiconductor chips, a semiconductor chip is now almost thinner than a lead frame. Such semiconductor chips have become highly dense, while densification of a semiconductor device mounting these semiconductor chips is insufficient. In particular, current semiconductor devices are not thin enough as thinning thereof has rarely received attention. Then, with a rapid prevalence of mobile data terminals like mobile phones, digital cameras, video camera and the like, there arise strong demands for downsizing and densification in consideration of the thickness of a semiconductor device. Downsizing and densification of a semiconductor device with its thickness reduced without an increase in area would provide desirable effects not only in such uses as mentioned above but in many other uses.